- Use a store base object to manage application state.
- Add a service to handle ajax requests.
- Load code only when needed

When reading conflicts:

1. Add a `type` field. `text` works as before, and has `sections`;
   `text-editor` is a file with ambiguous conflict markers that can only
   be resolved in an editor.
2. Add a `content_path` field pointing to a JSON representation of the
   file's content for a single file.
3. Hitting `content_path` returns a similar datastructure to the `file`,
   but without the `content_path` and `sections` fields, and with a
   `content` field containing the full contents of the file (with
   conflict markers).

When writing conflicts:

1. Instead of `sections` being at the top level, they are now in a
   `files` array. This matches the read format better.
2. The `files` array contains file hashes, each of which must contain:
   a. `new_path`
   b. `old_path`
   c. EITHER `sections` (which works as before) or `content` (with the
      full content of the resolved file).

Replace unique keyframes mixin with specific keyframe animation names

## What does this MR do?
Replaces `unique-keyframes` mixin with `include-keyframes` mixin

## Are there points in the code the reviewer needs to double check?
Shouldn't be 👍🏻 

## Why was this MR needed?
Some users had GitLab hosted in a distributed environment that makes `unique-keyframes` a non-viable implementation. 
The randomized animation names from `unique-keyframes` was not being picked up by the different servers which resulted in 404 errors.

## Screenshots (if relevant)
None

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?
Closes #22629

See merge request !6603

CE to EE merge check rake task

## What does this MR do?

This merge request adds a Rake task that checks whether the current branch can be merged cleanly to EE/master.

If not, it checks if a `<ce_branch>-ee` branch exists in EE, tries to merge it to EE/master and then tries to merge `ce_branch` to EE/master.

If the result of the check is that the current branch cannot be merged cleanly to EE/master, the job will fail, display troubleshooting steps, and a warning will be shown in the merge request.

## Are there points in the code the reviewer needs to double check?

Probably the steps I used to do the various checks, and also the steps I suggest to create an EE-specific branch.

## Why was this MR needed?

The goal is to catch as early as possible the possible conflicts a CE MR will cause when CE/master will be merged to EE/master. This way, the developer is warned that he/she should open a MR against EE before or as soon as the CE is merged. In the end, this should lower the work of the CE->EE merger.

## What are the relevant issue numbers?

Part of gitlab-org/gitlab-ee#715, hopefully.

See merge request !6746

Handle case where deployment ref no longer exists

## What does this MR do?

In 8.9, we didn't create keep-around refs for deployments. So it's possible that someone created a deployment (say, for testing), and then deleted the branch and all other references to that commit. That commit could then get GCed, and trying to view MRs on 8.11+ will show a 500. See https://gitlab.com/gitlab-org/gitlab-ce/issues/22655#note_16575020 for more details.

## Why was this MR needed?

If someone created a deployment on 8.9, then deleted all references to the commit for that deployment, we will throw an exception when checking if the deployment includes a commit.

Closes #22655.

See merge request !6855

Sort API mounts

## What does this MR do?

Sort the API mounts.

## Why was this MR needed?

The API mounts are unsorted.

See merge request !6831

Convert unicode emojis to images.

## Why was this MR needed?

For better cross platform interoperability with emojis.

Closes #22591

See merge request !6829

Also add a safeguard for non-CI env.
Signed-off-by: Rémy Coutable <remy@rymai.me>

Signed-off-by: Rémy Coutable <remy@rymai.me>